Solid dose delivery of bioactive materials to mucosal, dermal, ocular, subcutaneous, intradermal and pulmonary tissues offers several advantages over previous methods such as topical applications of liquids, transdermal administration via so-called “patches” and hypodermic injection. In the case of injection, solid dose delivery can reduce the risk of infection by eliminating the use of needles and syringes, provide for more accurate dosing than multidose vials, and minimize or eliminate the discomfort which often attends hypodermic injection. Several solid dose delivery systems have been developed including those utilizing transdermal and ballistic delivery devices.
Topical delivery is utilized for a variety of bioactive materials such as antibiotics for wound healing. These topical ointments, gels, creams, etc. must be frequently reapplied in order to remain effective. This is particularly difficult in the case of burn wounds.
Devices used for administering drugs transdermally usually comprise laminated composites with a reservoir layer of drug with the composite being adhered to the skin, i.e., transdermal patch, such as described in U.S. Pat. No. 4,906,463. However, many drugs are not suitable for transdermal delivery, nor have transdermal drug release rates for those capable of transdermal delivery been perfected.
Subdermal implants have also been formulated for slow release of certain pharmaceutical agents for extended periods of time such as months or years. A well-known example is the Norplant® for delivery of steroid hormones. Such implants are usually constructed of an inner, drug-filled core which is relatively permeable to the drug and an outer matrix which is relatively impermeable to the drug. Both inner core and outer matrix are generally formed from polymers. The implants release drugs by dissolution of the drug in the inner core and slow release across the outer matrix. The inner core may substantially dissolve over time, however, in devices currently in use, the outer matrix does not dissolve. Implants are placed subcutaneously by making an incision in the skin and forcing the implants between the skin and the muscle. At the end on their use, if not dissolved, these implants are surgically removed. U.S. Pat. No. 4,244,949 describes an implant which has an outer matrix of an inert plastic such as polytetrafluoroethylene resin. PCT/GB 90/00497 describes slow release vitreous systems for formation of implantable devices. These implants are bioabsorbable and need not be surgically removed. However, insertion is by surgical means. Moreover, these devices may be limited in the type of bioactive material that can be incorporated. In the case of polymeric implants, bioactive materials that cannot withstand organic solvents are not suitable for use. In the case of vitreous systems, bioactive materials that cannot withstand the elevated temperatures necessary to form the implants are unsuitable for use. In all cases, bioactive materials that are unstable at body temperature, particularly over long time periods, are unsuitable for use.
A variety of formulations have been provided for administration in aerosolized form to mucosal surfaces, particularly “by-inhalation” (naso-pharyngeal and pulmonary). Compositions for by-inhalation pharmaceutical administration generally comprise a liquid formulation of the pharmaceutical agent and a device for delivering the liquid in aerosolized form. U.S. Pat. No. 5,011,678 describes suitable compositions containing a pharmaceutically active substance, a biocompatible amphophilic steroid and a biocompatible (hydro/fluoro) carbon propellant. U.S. Pat. No. 5,006,343 describes suitable compositions containing liposomes, pharmaceutically active substances and an amount of alveolar surfactant protein effective to enhance transport of the liposomes across a pulmonary surface.
One drawback to the use of aerosolized formulations is that maintenance of pharmaceutical agents in aqueous suspensions or solutions can lead to aggregation and loss of activity and bioavailability. The loss of activity can be partially prevented by refrigeration; however, this limits the utility of these formulations. This is particularly true in the case of peptides and hormones. For instance, synthetic gonadotropin releasing hormone (GnRH) analogs, such as the agonist nafarelin or the antagonist ganirelex are designed for high potency, increased hydrophobicity and membrane binding. The compounds have sufficient hydrophobic character to aggregate in aqueous solution and to form an ordered structure that increases in viscosity with time. Thus bioavailability in nasal or pulmonary formulations may be prohibitively low. The use of powdered formulations overcomes many of these drawbacks. The requisite particle size of such powders is 0.5–5 microns in order to attain deep alveolar deposition in pulmonary delivery. Unfortunately, powders of such particle size tend to absorb water and clump and thus diminish deposition of the powder in the deep alveolar spaces. Although powders with larger particle size are suitable for delivery to the naso-pharynx region, the tendency of powders to clump decreases the available particle surface area for contact with, and absorption through, these membranes. Devices which disaggregate clumps formed by electrostatic interactions are currently in use (e.g., the Turbohaler™); however, these do not disaggregate moisture induced clumps and it would be advantageous to have powders which do not absorb moisture and clump and thus increase the effective pulmonary concentration of the drug.
Solid dose delivery vehicles for ballistic, transdermal, administration have also been developed. For example, in U.S. Pat. No. 3,948,263, a ballistic animal implant comprised of an exterior polymeric shell encasing a bioactive material is described for veterinary uses. Similarly, in U.S. Pat. No. 4,326,524, a solid dose ballistic projectile comprising bioactive material and inert binder without an exterior casing is disclosed. Delivery is by compressed gas or explosion. Gelatin covered tranquilizing substances carried by ballistic projectiles for implant are also described in U.S. Pat. No. 979,993.
The above-described ballistic devices, however, are suited to large animal veterinary applications due to their relatively large size, on the order of millimeters. Ballistic delivery at the cellular level has also been successful. The general principle of ballistic administration is the use of a supersonic wavefront, created by the release of compressed gas, to propel the particles contained in an adjoining chamber. For example, nucleic acids adsorbed on tungsten microprojectile particles have been successfully delivered to living epidermal plant cells. See Klein Nature 327:70–73 (1987). A better controlled device is the particle inflow gun (PIG). Vain et al. (1993) Plant Cell, Tissue and Organ Culture 33:237–246. Devices have been described which fire ampules containing medication using gas pressure. U.S. Pat. No. 4,790,824; and PCT/GB 94/00753. Several devices that inject fluids have also been described. U.S. Pat. Nos. 5,312,335 and 4,680,027. There are few existing formulations suitable for ballistic delivery. Powder formulations of pharmaceuticals in their present form are unsuitable for ballistic administration. Particles of available powder forms are generally irregular, varying in size, shape and density. This lack of uniformity leads to powder deposit and loss at the skin surface during administration, as well as problems in control and consistency of the depth of delivery to subcutaneous and intradermal tissues.
Thus it would be advantageous to provide solid dose drug delivery vehicles of defined size, shape and density, to ensure more uniform distribution. Additional benefits would accrue if the shape of the vehicle could be controlled to facilitate or control penetration of the epidermis and hard layers of the skin. Small delivery vehicle size, preferably coupled with high momentum delivery, would also increase the comfort of administration and minimize tissue damage. The manufacture of such a solid dose delivery vehicle should be such that neither the delivery vehicle nor the bioactive substance being delivered is damaged nor its efficacy decreased. Furthermore, the bioactive substance should remain stable when loaded within or on the vehicle so that efficacious administration can be achieved, and to facilitate storage of the loaded delivery vehicle. Manufacture of the solid dose delivery vehicle and its loading with bioactive material and the administration of the vehicle should also be relatively simple and economical.
All references cited herein are hereby incorporated by reference.